Attempting to fire 5.56x45mm NATO ammunition through a .300 AAC Blackout firearm is extremely dangerous and should never be attempted. While the two cartridges appear similar and can be chambered in AR-15 platform rifles, their dimensions differ significantly. The .300 Blackout utilizes a wider bullet diameter and the 5.56 NATO cartridge has a significantly higher chamber pressure. Firing a 5.56 round in a .300 Blackout chamber can lead to catastrophic weapon failure, potentially causing serious injury or even death to the shooter and those nearby.
Understanding the incompatibility of these cartridges is critical for safe firearm handling. The prevalence of the AR-15 platform, which can be adapted to numerous calibers, necessitates a clear understanding of the specific chambering of any given rifle. Confusion between calibers can have disastrous consequences. This highlights the importance of meticulously verifying ammunition compatibility before loading or firing any weapon. Safe gun ownership relies on the proper identification and use of correct ammunition.